Saints deserved to beat Cardiff, but suffered from a lack of cutting edge, according to Mauricio Pochettino.
The Welsh club launched a smash-and-grab raid at St Mary’s on Saturday, with Juan Cala’s second-half thunderbolt earning them a surprise three points.
Saints dominated the vast majority of the match against the relegation battlers, bossing in terms of both possession and chances.
Pochettino, therefore, felt that the result was an extremely harsh one, but he conceded that his side were made to pay for not being ruthless enough in front of goal.
“We created many chances, but we lacked a clinical edge that we actually needed to win the game,” said the Saints boss.
“It was the easiest game we’ve had in terms of possession.
“We had loads of possession, long spells of possession, but, in the end, it’s a steep learning curve when you realise that all that possession is useless when you don’t score a goal and that’s what we learned.”
Pochettino, who was also left to rue a fine performance from Cardiff keeper David Marshall, added: “If you analyse the game, you saw that Cardiff were defending with nine men behind the ball, and it’s really difficult to actually break that wall, that defence, when their defence is so close to their own goal.
“There were many spells where we were controlling the game.
“We had long spells of possession, their keeper made three or four brilliant saves that actually had a big factor in the game.
“I think, overall, it’s a game that we deserved a lot more (from).
“If you analyse, we should have won, but in the end it wasn’t to be for us.”
Pochettino had no complaints, however, about the defensive, counter-attacking tactics of his Cardiff counterpart, Ole Gunnar Solskjaer.
“I fully respect how the opposition sets up and I’m not going to judge how they set up,” he said.
“I will say that we had total control during the entire game, we created many chances.
“Their keeper made three or four outstanding saves, and it’s the type of game where you control, control, control the game and the time goes by.
“But you don’t get that breakthrough goal and then you end up losing on one of their plays.
“That seems innocuous at first, but in the end it does define the game.”